Comparisons of robotic ankle prosthesis and conventional prosthesis in below knee amputee

Abstract

Even though below knee amputees wear prosthesis, they show abnormal gait patterns and complain discomfort during everyday life. In this study we compared the gate pattern between robotic ankle-foot prosthesis and conventional prosthesis in patients with below knee amputation. Four patients with below knee amputation underwent gait analysis with wearing robotic prosthesis and conventional prosthesis. Our newly developed robotic ankle-foot prosthesis is based on a low weight unified actuator module. The low weight unified actuator module consists of a frameless BLDC (Bruchless direct current) motor, hall sensors, a harmonic drive, and a torque sensor. The robotic ankle provides necessary torque for different walking speed and walking surfaces. Gait analysis was done by VICON 3D motion analysis system (Oxford, England). Kinetics and kinematics data of cadence, speed, stride time, single-support time, stride length and step length during walking were assessed. Also rotational angle and moment of joint were assessed. In this study, wearing conventional prosthesis during walking, excessive gluteus maximus, tensor fascia lata activation was observed. However, wearing robotic ankle prosthesis, excessive hip abduction and external rotation was decreased. Also the weight shift between both side decreased due to increased trunk stability. A robotic ankle-foot prosthesis is required to provide a high output power within a compact size as well as to change its stiffness as dictated by the quasi-static stiffness of an intact ankle. The light weight integrated actuator module sufficiently supplied the torque source function to further enhance propulsion during powered plantar flexion. The embedded controller also provided the linear and nonlinear spring behaviors during controlled plantar flexion and dorsiflexion. As a result, robotic ankle prosthesis showed more normal gait pattern than conventional prosthesis. Robotic ankle prosthesis will be useful to improve quality of life in individuals with amputation. Further studies about robotic prosthesis is needed in rehabilitation medicine.